Internet users have come to expect nearly instantaneous response. Providing such responsiveness, particularly the responsiveness of web servers, depends on maintaining a favorable balance between resources and demands.
Resources to provide responsive Internet service have improved remarkably in the recent past. Faster processors and memories are available to both the users' workstations and the web sites' servers. Faster communication links are provided by optical fiber backbone transmission, cable-modem access, and asymmetric digital subscriber loop (ADSL) services.
Nevertheless, Internet responsiveness continues to be problematic, due to an ever-increasing burden that is placed on the Internet and on its web servers by an ever-increasing number of users and the ever-increasing sophistication of their demands. Moreover, patterns of Internet use may shift dramatically over a short time span, further complicating the problem of maintaining the delicate balance between resources and demands. For example, a breaking news story may lead to an avalanche of demand for related information, or halftime at a one sports event may lead to a flurry of queries for scores of other sports events ongoing at the same time, and so forth.
One way for a server to adapt to changing demand involves keeping and using logbooks that record past activities. Based on data kept in the logbooks, the server determines which web pages it should make readily available by storing in its cache memory rather than in its main memory. Unfortunately, logbooks of past activities are often large, cumbersome, and slow to adjust to short-term changes in web server demands. Consequently, when demand changes abruptly, the server is caught with the wrong pages stored in cache, and clients must endure delay while the server laboriously retrieves pages form main memory rather than from cache.
Thus, in view of the shortcomings associated with the use of logbooks and the desirability of providing responsive web servers, there is a need for a way of tracking nearly instantaneous changes in demands on web sites, so that web servers may adapt their cache memories to short-term demand changes and reconfigure their resources quickly, in order to provide the most responsive services possible.